Corn kernels have three main parts, the seed coat or pericarp, the starchy endosperm, and the embryo, commonly called the germ. The pericarp is the outer skin or hull of the kernel which serves to protect the seed. The endosperm, the main energy reserve, makes up about 80% of the total weight of the kernel. It is about 90% starch and 7% gluten (protein), with the remainder consisting of small amounts of oil, minerals and some trace constituents. The embryo contains a miniature plant made up of a root-like portion and five or six embryonic leaves. In addition, there are large quantities of high energy oil to feed the tiny plant when it starts to grow, as well as many substances required during germination and early development.
Starch is one of nature's major renewable resources and a mainstay of food and industrial economy. Basic consumer necessities such as paper and textiles are major uses for corn starch in sizing, surface coating and adhesive applications.
For more than 150 years, corn refiners have been perfecting the process of separating corn into its component parts to create a myriad of value added products. The corn wet milling process separates corn into four main components: starch, germ, fiber and protein.
An overview of wet milling process is illustrated in the FIG. 4 annexed herewith. Typically, the process comprises five basic steps:                cleaning;        steeping;        germ separation;        grinding and screening; and        starch separation.        
The first step in the process consists in cleaning the grain to remove extraneous material such as pieces of cob, foreign seeds, fine dirt, and other light unwanted material.
The cleaned corn is further soaked in 50 degree water, usually containing small quantities of dissolved sulfur dioxide to prevent excessive bacterial growth, for 30 to 40 hours in steep tanks. During “steeping”, the kernels absorb water, increasing their moisture levels from 15 percent to 45 percent and more than doubling in size. As the corn swells and softens, the mild acidity of the steepwater begins to loosen the gluten bonds within the corn and release the starch. After steeping, the corn is coarsely ground to break the germ loose from other components.
Water is added to the attrition mills and a thick slurry of macerated kernels and whole germ results. Because the germ at this stage contains 40-50% oil (about 85% of total corn oil) it is lighter than the endosperm and hull. The “germ separation” is thus achieved using centrifugal force to isolate the germ.
The remaining mixture of hull and endosperm then passes through a series of “grinding” and “screening” operations to release the starch and gluten from the fiber In the kernel. The suspension of starch, gluten and fiber is flowed over fixed screens which catch fiber but allow starch and gluten to pass through.
The water slurry of starch and gluten is further separated by centrifugation. Because starch and gluten differ in density, almost complete “starch separation” is obtained. The starch, with just one or two percent protein remaining, is diluted, washed 8 to 14 times, rediluted and washed again to remove the last trace of protein and produce highly pure starch.
Typical operations yield a starch stream over 99% pure starch, usually more than 99.5% pure starch. The overall yield of the wet milling process is at least 95% of starch initially present in corn grain.
The time required to conduct the totality of these operations is in theory up to 48 hours. In practice, many millers claim it usually takes about 36 hours or more to them to get over 95% of the starch out through this process.
A reduction of the milling time while maintaining same starch yield would be of great industrial interest. Actually, such a reduction would increase milling plants capacity and thus reduce cost per unit of starch extracted.